woodbridge



313=- +l4e GR 297359031 Feb. 14, 1956 Filed Feb. 5, 1952 8 7 9 l4 I5 I SEARQH .ROQNQ L. A. WOODBRIDGE 2,735,031

CATHODE RAY TUBES 2 Sheets-Sheet l mnfir LEONARD ALBERT WOODBR/DGE OPDLZ M 6% hrfnrnpy Feb. 14, 1956 A. WOODBRIDGE 2,735,031

CATHODE RAY TUBES Filed Feb. 5, 1952 2 Sheets-Sheet 2 hive/775w LEONARD ALBERT WOODBR/DGE United States Patent CATHODE RAY TUBES Leonard Albert Woodbridge, Beaconsfield, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application February 5, 1952, Serial No. 269,931

Claims priority, application Great Britain February 15,- 1951 8 Claims. (Cl. 313-70) This invention relates to cathode ray tubes.

The life of a cathode ray tube generally ends when the emissivity of the cathode has fallen below a useful value, or when the cathode heater fails. The object of the invention is to provide a cathode ray tube having a longer life than cathode ray tubes of conventional construction.

According to the invention, a cathode ray tube comprises a plurality of independent cathodes arranged about the axis of said tube and capable of being energized separately, a first deflecting means for directing the electrons emitted by any particular one of said cathodes when energized in one direction and second deflecting means for directing said deflected electrons in an opposite direction, thereby to cause said electrons to follow a path substantially coincident with the axis of said tube.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawings, in which:

Figure 1 illustrates by way of example one form of cathode ray tube provided with a fluorescent screen such as is suitable for use in television receivers according to the invention.

Figures 2 and 3 illustrate in greater detail the cathode structure of the tube shown in Figure 1, Figure 2 being a section on line 2-2 of Figure 3.

Figures 4 and 5 illustrate a modified cathode structure, Figure 4 being a cross section on the line 44 of Figure 5,

Figure 6 illustrates a cathode ray tube with the form of cathode structure shown in Figures 4 and 5, and

Figure 7 illustrates a modified cathode structure according to the invention.

The envelope of the cathode ray tube illustrated in Figure 1 is of conventional form and comprises a neck portion 1 joined to an enlarged portion 2 the inner surface of the end wall of which is coated with fluorescent material in known manner, the other end of the neck 1 being closed by means of a contact carrying pinch 3 of disc form. A coating 4 of metal or graphite is provided on the internal wall of the neck 1 and part of the portion 2 and serves in known manner as an anode electrode. At a suitable position along the neck 1 there is provided focussing means 5 which may be a coil or an annular permanent magnet. Within the neck 1 close to the pinch 3 there is arranged a cathode structure according to the invention, the details of which will now be described with reference to Figures 2 and 3.

An insulating disc 6 is provided with four apertures angularly disposed about its axis and into these apertures are secured four cathodes 7 each of which is provided on the outer surface of its closed end with a coating of electron emissive material. Within the tubular part of each of the cathodes 7 there is arranged a suitable heating element 8 such as a tungsten wire coated with an adherent layer of refractory insulation. The insulating disc 6 with the cathodes 7 assembled in it, is mounted within a modulator electrode 9 the end wall 10 of which is provided with four small apertures 11 so that each of them is co-axial with a corresponding cathode 7.

Suitable shields may be arranged between the cathodes 7 in order to minimize evaporation from any one cathode affecting the others and such a shield may conveniently be formed by welding two V-shaped metal strips 12 to the underside of the modulator end wall 10 so that they project towards the insulator 6.

Adjacent to the modulator 9 is disposed an anode electrode 13 provided with four apertures 14 each being several times the diameter of the apertures 11 in the modulator 9 said apertures 14 being disposed so that they are opposite the apertures 11 in the modulator 9 such that if the apertures 11 were projected, part of their peripheries would touch or almost touch an inner edge of the corresponding aperture 14 at a position towards the axis of the anode 13 as shown in Figure 3.:

The electrodes above described are assembled together as a unitary structure and mounted within the envelope of a cathode ray tube so that the axis of the modulator is in line with the axis of the tube.

Referring again to Figure l the various electrode elements are connected to the contact pins passing through the pinch 3 and in this example seven pins would be provided, one leg of each heating element 8 being connected to a common pin the other leg of each heater 8 being taken to separate pins. One of the two remaining pins is connected to the modulator 9 and the other serving as a common connection for the four cathodes 7. With tubes for certain applications, it may be found that the added capacity due to the provision of the four cathodes 7 connected together is undesirable and in these tubes extra pins may be provided, so that each cathode 7 may be connected to an individual pin.

In operation of the tube the heater 8 of one of the cathodes 7 is connected to a suitable source of supply and the anode 13 is maintained positive with respect to the modulator 9 and cathode 7 so that electrons emitted by the cathode are drawn through the associated small aperture 11 towards and through the corresponding aperture 14 in the anode 13 as a diverging beam. The electrostatic field set up between the apertures 11 and 13 is asymmetrical and will cause the electrons and any charged particles present in the beam to proceed in a direction across the axis of the tube as shown at a. Arranged at a suitable position along the outside neck 1 of the tube is a magnet assembly 15 oriented so that the field set up by it will direct the electrons in the beam in a direction opposite to that imposed on it by the electrostatic field set up by the modulator 9 and anode 13 so that the electrons will proceed substantially along the axis of the tube and will be brought to a focus on the fluorescent screen by the focussing means 5.

The magnet assembly 15 preferably comprises a pair of block permanent magnets secured at apart on to the inner surface of a soft iron ring with poles of opposite polarity facing each other. The pole surfaces of the assembly 15 make a close fit with the external wall of the neck 1 and are positioned so that the lines of force extend across the neck 1 of the tube and such lines of force will be, in the example shown in Figure 1, in a direction which is normal to the plane of the drawing.

In the drawing the magnet assembly 15 is shown spaced a considerable distance from the anode 13 in order to clearly show the bending of the beam, but in actual practice this magnet assembly would be positioned close to and mainly in line with the anode 13. Deflection of the focussed beam over the screen of the tube is accomplished by means of deflecting coils indicated diagrammatically at 16, to which are applied during operation of the tube suitable currents of sawtooth waveform in well known manner.

The life of each of the cathodes 7 will be substantially the same as those normally employed, and when the emissivity of one cathode has fallen below a useful value, or when the heater 8 fails, another cathode may be employed in its place by connecting the heater of said other cathode to the supply source, the magnet 15 being suitably rotated about the neck 1 of the envelope so as to position the magnet with respect to the electron beam issuing from the particular cathode being used. With the arrangement described the cathode ray tube may have a life approximately four times as long as that of a tube provided with a single cathode. Occasionally when the manufacture of a tube has been completed it is found that the cathode is not sufficiently emissive and the tube has to be rejected. It is, however, extremely unlikely that in a tube according to the invention all of the cathodes 7 would be found to be unsatisfactory and the invention therefore reduces very considerably the risk of tubes being rejected.

A modification of the above described arrangement is shown in Figures 4, and 6 and in these figures parts which are the same as those previously described are given the same reference numerals.

As shown in Figures 4 and 5 the cathode-modulator assembly is identical with that previously described in connection with Figure 2 but the anode electrode 13 instead of having four angularly disposed apertures is provided with a single central aperture 17. The aperture 17 is arranged to be of a radius at least as great as that of the circumscribing circle of the four small apertures 11 in the end wall of the modulator 9.

Referring now to the cathode ray tube shown in Figure 6: when the heater element 8 of one of the cathodes 7 is connected to a suitable source of supply and the anode 13 is maintained at a positive potential with respect to the modulator 9 and cathode 7, the asymmetric electrostatic field set up between the corresponding aperture 11 in the modulator 9 and the aperture 17 in the anode 13 causes the electrons and any charged particles in the beam to move in a direction away from the axis of the tube as shown at b. In order to direct the electron beam on to or parallel with the axis of the tube an external magnetic deflecting field 18 is provided and this may conveniently be a permanent magnet assembly which is identical with 15 employed in Figure l and positioned so that the field set up by it will deflect the electrons of the beam in a direction towards the tube axis. If desired a further similar magnet assembly 19 may be provided so that the electron beam where it meets the tube axis is deflected slightly, to ensure that the electrons will proceed along the tube axis. The magnet assemblies 18 and 19 will be arranged so that the magnetic lines of force extend across the neck 1 of the tube i. e. in a direction normal to the plane of the drawing.

As previously mentioned in connection with Figure 1 the magnet assembly 18 is shown spaced from anode 13 in order to show clearly the bending of the beam, but in actual practice this magnet assembly would be positioned substantially in line with the anode 13.

In each of the above-described arrangements an additional anode may be included in order to provide an electron-gun of the tetrode type. In such cases the arrangement may be similar to either of those described above with the addition as illustrated in Figure 7 of a further anode 20 disposed between the modulator 9 and anode 13. The additional anode 20 is provided with apertures 21 corresponding in arrangement to the apertures 11 in the modulator end wall 10 the said apertures 11 and 21 being preferably of the same size.

Such an electrode structure may be employed in a cathode ray tube as shown in Figure 1 or Figure 6, connection being made to this anode 20 by means of an additional contact pin provided in the pinch 3 so that during operation of the tube it may be maintained at a positive potential which is lower than that of the anode 13.

When under the action of said magnet assembly 15 Figure l or magnet assemblies 18 and 19 Figure 6 the beam is deflected towards or along the axis of the cathode ray tube, any ions in the beam are substantially undeflected and they therefore continue along the initial path of the beam. However means may be provided for collecting said ions and said means may be formed by attaching a tubular extension to the anode 13 so that it extends in a direction away from the cathodes 7.

Although in the above description cathode ray tubes having four independent cathodes have been described it will be understood that cathode ray tubes which are provided with two or more independent cathodes are within the scope of the invention.

What I claim is:

l. A cathode ray tube comprising a plurality of indedependent cathodes capable of being selectively energised at will the electron streams from which are each adapted to pass through an aperture in a first electrode and then through an aperture in an adjacent electrode, the aperture in said latter electrode having its centre offset with respect to the centre of said first-mentioned aperture, circuit connections to said electrodes for setting up therebetween a constant electrostatic field to cause the electron stream passing therethrough to be deflected in respect of a desired path for said stream whereby if a further suitable constant deflecting field is set up in the vicinity of said electrodes, the electron stream from any one of said cathodes is caused to move first in one direction and then in a chal liged direction so as thereafter to follow said desired pat 2. A cathode ray tube provided with a plurality of cathodes capable of being energized separately and mounted in said tube with said cathodes disposed about the axis thereof, a pair of electrodes each having apertures corresponding in number with said cathodes, the first electrode of said pair being disposed nearer said cathodes with its apertures in alignment therewith, and said second electrode of said pair having apertures larger in diameter than the corresponding apertures in said first electrode and with centres offset with respect to the centres of corresponding apertures in said first electrode.

3. A cathode ray tube according to claim 2, including a further electrode between said cathodes and said pair of electrodes, said further electrode having a plurality of apertures one for each cathode, said apertures being arranged coaxially with the apertures in said first electro e.

4. A cathode ray tube provided with a plurality of cathodes capable of being energized separately and mounted in said tube with said cathodes disposed about the axis thereof, a pair of electrodes, the first electrode of said pair being nearer said cathodes and being formed with apertures corresponding in number with said cathodes and aligned with said cathodes, the second electrode of said pair being arranged adjacent said first electrode, said second electrode being formed with a single aperture having a larger diameter than any of the apertures in said first electrode, and the centre of the aperture in said second electrode being arranged substantially coincident with the axis of said tube.

5. A cathode ray tube according to claim 4, the diameter of said single aperture in said second electrode being proportioned to circumscribe all the apertures in said first electrode.

6. A cathode ray tube according to claim 4, including a further electrode between said cathodes and said pair of electrodes, said further electrode having a plurality of apertures one for each cathode, and said apertures being arranged coaxially with the apertures in said first electrode of said pair of electrodes.

7. A cathode ray tube provided with a plurality of cathodes capable of being energized separately and mounted in said tube with said cathodes disposed about the axis thereof, a pair of electrodes each having apertures corresponding in number with said cathodes, the first electrode of said pair being disposed nearer said cathodes with its apertures in alignment therewith, and said second electrode of said pair having apertures larger in diameter than the corresponding apertures in said first electrode and with centres oflset with respect to the centres of corresponding apertures in said first electrode, circuit connections for setting up an electrostatic field between said pair of electrodes to deflect electrons from an energized cathode in a direction away from the axis of said cathode, and magnetic means for deflecting said deflected electrons in an opposite direction to follow a path substantially coincident with the axis of said tube.

8. A cathode ray tube provided with a plurality of cathodes capable of being energized separately and mounted in said tube with said cathodes disposed about the axis thereof, a pair of electrodes, the first electrode of said pair being nearer said cathodes and being formed with apertures corresponding in number with said cathodes and aligned with said cathodes, a second electrode of said pair adjacent said first electrode, said second electrode being formed with a single aperture having a larger diameter than any of the apertures in said first electrode, the centre of the aperture in said second electrode being arranged substantially coincident with the axis of said tube, circuit connections for setting up an electrostatic field between said pair of electrodes to deflect the electrons from an energized cathode in a direction away from the axis of said cathode, and magnetic means for deflecting said deflected electrons in an opposite direction to direct said electrons in a path substantially coincident with the axis of said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,083,203 Schlesinger June 8, 1937 2,170,944 Glass et al Aug. 29, 1939 2,205,071 Skellett June 18, 1940 2,227,484 Bouwers Ian. 7, 1941 2,348,133 Iams May 2, 1944 2,457,175 Parker Dec. 28, 1948 2,612,614 Amdursky et al. Sept. 30, 1952 2,660,612 Wood, Jr. Nov. 24, 1953 2,669,675 Lawrence Feb. 16, 1954 FOREIGN PATENTS 866,065 France Mar. 31, 1941 

